Article

Analysis and retrieval of tropospheric corrections for CryoSat-2 over inland waters

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Abstract

The application of satellite altimetry over inland waters requires a proper modelling of the various error sources involved in the determination of precise surface water heights above a reference ellipsoid or above the geoid. The objectives of this study are firstly the analysis of the errors present on the dry tropospheric correction (DTC) and on the wet tropospheric correction (WTC) provided in the CryoSat-2 (CS-2) products and secondly the development of methodologies to derive improved corrections, aiming at getting improved products for CS-2. This study is conducted on selected regions of interest, such as the Amazon and Danube rivers, Titicaca and Vanern lakes and the Caspian Sea. Since CS-2 has a geodetic orbit, its ground tracks allow the retrieval of precise surface water heights over regions not covered by any other satellite. The DTC and WTC present in the CS-2 products have been compared against corrections computed from the European Centre for Medium-Range Weather Forecasts (ECMWF) operational model at various levels: (i) the level of ECMWF model orography; (ii) the level of the Altimetry Corrected Elevations 2 (ACE2) digital elevation model and (iii) the level of mean lake/sea or river profile. An independent assessment of the corrections has also been performed by comparison with DTC derived from in situ surface pressure measurements and WTC retrieved from Global Navigation Satellite Systems (GNSS) data. Results show that the model-derived corrections present on CS-2 products seem to be referred to the model orography, except for the Caspian Sea where corrections seem to be referred to mean sea level (zero level). Model orography can depart from the mean river profile or mean lake/sea heights by hundreds of meters. Overall, ACE2 DEM is a better altimetric surface than ECMWF orography, however height errors up to hundreds of meters exist in ACE2. Height errors induce DTC errors that can reach several centimetres (11 cm in the Danube River) and WTC errors up to 2–3 cm. These errors are systematic, having always the same sign and magnitude for a given location, thus affecting the retrieval of the absolute water level. For rivers, the mean profile is the best representation of the surface height in the river basin and is also the best reference surface for use in the DTC and WTC estimations from an atmospheric model. The same happens with lakes or closed seas, where the corrections should be referred to the mean lake/sea level. Results show that, once computed at the correct mean river profile or mean lake/sea level, the DTC has a small variation, with a standard deviation going from 0.5 cm in the Amazon River to 3.0 cm in the Danube River. The DTC absolute values go from 1.48 m in Lake Titicaca to 2.32 m in the Caspian Sea. With a larger variability, once computed at mean river profile or mean lake/sea level, the standard deviation of the WTC goes from 2.7 cm in Lake Titicaca to 5–6 cm in all other regions and absolute values from only 6 cm in Lake Titicaca to 31 cm in the Amazon River. Once computed at the correct surface elevation the corresponding errors are expected to be less than 1 cm for the DTC and less than 2 cm for the WTC.

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... Due to this complex 4-D variation, for altimetry applications over open-ocean, the WPD is best determined from collocated measurements provided by Microwave Radiometers (MWR), passive instruments on board most of altimetric missions [7]. Satellite altimetry has been used over coastal [8-10] and inland waters [5,11], however the WPD retrievals from MWR measurements become invalid and cannot be used over these regions [12]. The current algorithms that compute the WPD from MWR measurements have been tuned to conditions only over ocean surfaces [13]. ...
... The global assessment with ERA5 data and mainly the validation with in situ radiosondes at vertical levels show the significant impact of the modelling presented in this study, when compared with the only modelling available so far [20]. The new UP models must be adopted to reduce WPD values at undesirable altitudes, e.g., those provided at the level of NWM orography in some altimetry products [5,11]. One of the applications of these models will be the integration in the GNSS-derived Path Delays Plus (GPD+) algorithm [16][17][18], which provides valid WPD measurements whenever the corresponding path delay derived from MWR is invalid or inexistent. ...
... This method combines The global assessment with ERA5 data and mainly the validation with in situ radiosondes at vertical levels show the significant impact of the modelling presented in this study, when compared with the only modelling available so far [20]. The new UP models must be adopted to reduce WPD values at undesirable altitudes, e.g., those provided at the level of NWM orography in some altimetry products [5,11]. One of the applications of these models will be the integration in the GNSS-derived Path Delays Plus (GPD+) algorithm [16][17][18], which provides valid WPD measurements whenever the corresponding path delay derived from MWR is invalid or inexistent. ...
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... Adopting this methodology, the DTC can be determined for any surface type with an accuracy better than 1 cm. It has been shown that it is better to use SLP instead of SurfP, as the latter usually leads to Gibbs effects in the corrections (Fernandes et al., 2014;Vieira et al., 2018). ...
... In regions such as inland waters, GNSS may be the best source for WTC retrieval (Fernandes et al., 2014;Vieira et al., 2018). In addition, GNSS plays a major role in filling the gap left by MWR in coastal regions (see section 4.3.4). ...
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... Amidst these terms is the wet tropospheric correction (WTC), due to the water vapour and liquid water content in the atmosphere. Since these variables have large space-time variability, if not properly modelled, the WTC is one of the major sources of uncertainty in many satellite altimetry applications [13,15,16]. ...
... In addition to the native S3A products, the website includes the orbit and state-of-the-art range and geophysical corrections present in RADS for all other altimeter missions. The data span approximately 10 months, from 15 June 2016 (cycle 05) to 15 April 2017 (cycle 16). ...
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... However, over some regions, e.g. inland waters (Vieira et al. 2018), NWM can be the only source available and should be used (Fernandes et al. 2021(Fernandes et al. , 2014. Moreover, the quality of the atmospheric models commonly used to compute the tropospheric corrections has been increasing over time, by means of improved data and assimilation methodologies. ...
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... It has long been recognized that due to this high variability, the best and most accurate way to measure this effect over the open ocean is from collocated microwave radiometer (MWR) measurements, a passive instrument onboard most of altimetric missions. However, WPD retrievals from MWR measurements become systematically invalid and cannot be used over some regions, such as coastal zones [6], [7] and inland waters [4], [8]. On the other hand, some satellites (e.g., CryoSat-2) do not possess an MWR in their payload. ...
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... These models provide similar results to the study of Davis et al. (1985) (that uses 3-D parameters) but only at the level of the model orography to which the meteorological parameters refer to. As this orography may depart significantly from the actual surface, and the vertical variation of the ZWD is not well known, at a different elevation they possess errors associated with the uncertainty in the modelling of the ZWD height variation (Fernandes et al., 2013(Fernandes et al., , 2014Vieira et al., 2018). The traditional Saastamoinen model (1972) andHopfield model (1971) approximate the ZWD with surface observations as temperature and water vapour pressure observations. ...
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The empirical model GPT (Global Pressure and Temperature), which is based on spherical harmonics up to degree and order nine, provides pressure and temperature at any site in the vicinity of the Earth’s surface. It can be used for geodetic applications such as the determination of a priori hydrostatic zenith delays, reference pressure values for atmospheric loading, or thermal deformation of Very Long Baseline Interferometry (VLBI) radio telescopes. Input parameters of GPT are the station coordinates and the day of the year, thus also allowing one to model the annual variations of the parameters. As an improvement compared with previous models, it reproduces the large pressure anomaly over Antarctica, which can cause station height errors in the analysis of space-geodetic data of up to 1cm if not considered properly in troposphere modelling. First tests at selected geodetic observing stations show that the pressure biases considerably decrease when using GPT instead of the very simple approaches applied to various Global Navigation Satellite Systems (GNSS) software packages so far. GPT also provides an appropriate model for the annual variability of global temperature.
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The new gridded Vienna Mapping Function (VMF1) was implemented and compared to the well-established site-dependent VMF1, directly and by using precise point positioning (PPP) with International GNSS Service (IGS) Final orbits/clocks for a 1.5-year GPS data set of 11 globally distributed IGS stations. The gridded VMF1 data can be interpolated for any location and for any time after 1994, whereas the site-dependent VMF1 data are only available at selected IGS stations and only after 2004. Both gridded and site-dependent VMF1 PPP solutions agree within 1 and 2mm for the horizontal and vertical position components, respectively, provided that respective VMF1 hydrostatic zenith path delays (ZPD) are used for hydrostatic ZPD mapping to slant delays. The total ZPD of the gridded and site-dependent VMF1 data agree with PPP ZPD solutions with RMS of 1.5 and 1.8cm, respectively. Such precise total ZPDs could provide useful initial a priori ZPD estimates for kinematic PPP and regional static GPS solutions. The hydrostatic ZPDs of the gridded VMF1 compare with the site-dependent VMF1 ZPDs with RMS of 0.3cm, subject to some biases and discontinuities of up to 4cm, which are likely due to different strategies used in the generation of the site-dependent VMF1 data. The precision of gridded hydrostatic ZPD should be sufficient for accurate a priori hydrostatic ZPD mapping in all precise GPS and very long baseline interferometry (VLBI) solutions. Conversely, precise and globally distributed geodetic solutions of total ZPDs, which need to be linked to VLBI to control biases and stability, should also provide a consistent and stable reference frame for long-term and state-of-the-art numerical weather modeling.
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We present a new approach to remote sensing of water vapor based on the Global Positioning System (GPS). Geodesists and geophysicists have devised methods for estimating the extent to which signals propagating from GPS satellites to ground-based GPS receivers are delayed by atmospheric water vapor. This delay is parameterized in terms of a time-varying zenith wet delay (ZWD) which is retrieved by stochastic filtering of the GPS data. Given surface temperature and pressure readings at the GPS receiver, the retrieved ZWD can be transformed with very little additional uncertainty into an estimate of the integrated water vapor (IWV) overlying that receiver. Networks of continuously operating GPS receivers are being constructed by geodesists, geophysicists, and government and military agencies, in order to implement a wide range of positioning capabilities. These emerging GPS networks offer the possibility of observing the horizontal distribution of IWV or, equivalently, precipitate water with unprecedented coverage and a temporal resolution of the order of 10 min. These measurements could be utilized in operational weather forecasting and in fundamental research into atmospheric storm systems, the hydrologic cycle, atmospheric chemistry, and global climate change.
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The Global Reservoir and Lake Monitor (GRLM) records variations in surface water height for approximately 70 lakes and reservoirs worldwide using a combination of satellite radar altimetry data sets. The project was initiated by the U.S. Department of Agriculture’s (USDA) Foreign Agricultural Service (FAS) in cooperation with the National Aeronautic and Space Administration’s (NASA) Goddard Space Flight Center (GSFC) and the University of Maryland (UMD). On-line since the end of 2003, the program focuses on the delivery of near-real-time products within an operational framework and exists within the USDA’s decision support system (DSS) through the larger cooperative USDA/NASA Global Agricultural Monitoring (GLAM) program. Currently, near-real-time products are derived from the NASA/Centre National d’Etudes Spatiales (CNES) Jason-1 mission (post-2002) with archival products derived from the NASA/CNES TOPEX/Poseidon mission (1992–2002) and the US Naval Research Lab’s (NRL) Geosat follow-on (GFO) mission (2000–2008). Validation exercises show that the products vary in accuracy from a few centimeters RMS (root mean square) to several tens of centimeters RMS depending on the target size and surface wave conditions. On a weekly basis, new satellite data are retrieved and products updated. Output is in the form of graphs and text files with web links to other imaging and information resources. The next phase of the program sees an expansion to over 500 lakes and reservoirs via the incorporation of products derived from the European Space Agency (ESA) remote sensing satellites (ERS-1 and ERS-2, 1992–2008) and the ESA environmental satellite ENVISAT (post-2002). Near-real-time products will also be continued via data from the follow-on Jason-2 mission (post-2009). The USDA/FAS utilize the products for irrigation potential considerations and as general indicators of drought and high-water conditions. The monitoring system thus has relevance to water resources management and agriculture efficiency at both the national and international level.
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Tide gauge measurements recorded between 1978 and 1993 indicate that the Caspian sea level (CSL) has been rising at an average rate of ∼12 cm/yr during this 15-yr time span. Decadal CSL changes are currently attributed to changes in river runoff and effective evaporation. We have analysed three and a half years (from January 1993 through August 1996) of altimeter range data from the TOPEX-POSEIDON mission over the Caspian sea to estimate temporal variations in the sea level. We show that the Caspian sea level was still rising at a rate of 18.9 ± 0.5 cm/yr between January 1993 and July 1995 and that the northwestern Caspian in the area of the Volga delta was rising faster (by ∼3 cm/yr) than the middle and south Caspian. However, by mid-1995, the CSL started to drop abruptly, a trend still observed in 1996. The average sea level decrease recorded from mid-1995 amounts to -24.8 ± 1.4 cm/yr.
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This study presents the results of calibration/validation (C/V) of Envisat satellite radar altimeter over Lake Issykkul located in Kyrgyzstan, which was chosen as a dedicated radar altimetry C/V site in 2004. The objectives are to estimate the absolute altimeter bias of Envisat and its orbit based on cross-over analysis with TOPEX/Poseidon (T/P), Jason-1 and Jason-2 over the ocean. We have used a new method of GPS data processing in a kinematic mode, developed at the Groupe de Recherche de Geodesie Spatiale (GRGS), which allows us to calculate the position of the GPS antenna without needing a GPS reference station. The C/V is conducted using various equipments: a local GPS network, a moving GPS antenna along the satellites tracks over Lake Issykkul, In Situ level gauges and weather stations. The absolute bias obtained for Envisat from field campaigns conducted in 2009 and 2010 is between 62.1 and 63.4 ± 3.7 cm, using the Ice-1 retracking algorithm, and between 46.9 and 51.2 cm with the ocean retracking algorithm. These results differ by about 10 cm from previous studies, principally due to improvement of the C/V procedure. Apart from the new algorithm for GPS data processing and the orbit error reduction, more attention has been paid to the GPS antenna height calculation, and we have reduced the errors induced by seiche over Lake Issykkul. This has been assured using cruise data along the Envisat satellite track at the exact date of the pass of the satellite for the two campaigns. The calculation of the Envisat radar altimeter bias with respect to the GPS levelling is essential to allow the continuity of multi-mission data on the same orbit, with the expected launch of SARAL/Altika mission in 2012. Implications for hydrology in particular, will be to produce long term homogeneous and reliable time series of lake levels worldwide.
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Spectral atmospheric general circulation models (GCMs) have been used for many years for the simulation and prediction of the atmospheric circulation, and their value has been widely recognized. One of their major drawbacks is the inability of the spectral spherical harmonics transform to represent discontinuous features, resulting in Gibbs oscillations. Two applications of a filter technique are presented. In the first application the method is applied to the orography field by filtering out sharp gradients or discontinuities. The numerical results with this method show some improvement in the cloud and precipitation fields, along with some improvement of the surface wind pattern, resulting in an overall better simulation. In the second application, a Gibbs reduction technique is applied to the condensation process. In this paper the moist-adiabatic adjustment scheme is used for the cumulus parameterization, in addition to large-scale condensation. Numerical results with this method to reduce Gibbs oscillations due to condensation show some improvement in the distribution of rainfall, and the procedure significantly reduces the need for negative filling of moisture. The negative moisture areas at high latitudes can be, to some extent, controlled by an empirical procedure, but the filter approach is not sophisticated enough to satisfactorily remove the complex Gibbs oscillations present in the condensation field. -from Authors
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Remote sensing and long-term monitoring of closed and climatically sensitive open lakes can provide useful information for the study of climatic change. Satellite radar altimetry offers the advantages of day/night and all-weather capability in the production of relative lake level changes on a global scale. A simple technique which derives relative lake level changes is described with specific relevance to the TOPEX/POSEIDON geophysical data record data set. An assessment of the coverage and global tracking performance of both the NASA radar altimeter and the solid state altimeter over these lakes is discussed, and results are presented for the first 1.75 years of the mission. Lake level time series were acquired for 12 closed lakes, six open lakes, and three reservoirs, providing information in many cases where ground gauge data are unobtainable or the lake is inaccessible. The results, accurate to ˜4 cm rms, mark the beginning of a very accurate lake level data set, showing that TOPEX/POSEIDON can successfully contribute to the long-term global program.
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This paper presents an application of the TOPEX/Poseidon (T/P) satellite altimetry data to estimate river discharge at three sites along the Amazon River. We discuss the methodology to establish empirical relationships between satellite-derived water levels and daily estimations of river discharges based on rating curves and in situ level measurements at gauging stations. Three sites are chosen: Manacapuru (River Solimões), Jatuarana (nearby the confluence of the Solimões and Rio Negro rivers) and Óbidos (Amazon River). We then reconstruct the satellite-based river discharge over a 10-year time span (1992–2002). Comparison between satellite-derived and river discharge at the gauging stations shows that the T/P data can successfully be used for hydrological studies of large rivers, in providing in particular discharge estimates when in situ data are not available. To cite this article: E.A. Zakharova et al., C. R. Geoscience 338 (2006).
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Monitoring continental water flows is required to meet human needs and to assess ongoing climate changes. However, regular gauging networks fail to provide the information needed for spatial coverage and timely delivery. Although the missions did not initially focus on hydrology, ten years of satellite altimetry have furnished complementary data that can be used for the creation of such hydrological products as time series of stages, discharges, river altitude profiles or levelling of in-situ stations. However, raw data still suffer uncertainties from one to several decimetres and require specific reprocessing of raw data, such as waveform retracking or geophysical correction editing. To cite this article: S. Calmant, F. Seyler, C. R. Geoscience 338 (2006).
Article
For more than 10 years, satellite radar altimetry has been a successful technique for monitoring the variation in elevation of continental surface water, such as inland seas, lakes, rivers, and more recently wetland zones. The surface water level is measured within a terrestrial reference frame with a repeatability varying from 10 to 35 days depending on the orbit cycle of the satellite. With several decades of technique refinement, current data processing can be fairly simple or complex depending on the mission and the instrument tracking methods. Data acquisition is not affected by weather conditions, but the technique can have a number of limitations. Rapidly varying topography or complex terrain may inhibit the retrieval of good elevation data. The instruments can only operate in a profiling mode and do not have a true global view. Stage accuracies are also dependent on target size and surface roughness, which will limit worldwide surveying and limnological applications. However, there is the scope for systematic continental scale monitoring and the provision of new stage information where gauge data is absent. The technique is sufficiently advanced to have enabled a number of inland water case studies. Focussing on the large lakes, the links between lake evolution and the local climate cycle on seasonal to interannual timescales have been explored, and water storage balance for water management has also been brought into focus. Typically altimetric stage measurements can range in accuracy from a few centimetres (e.g., Great Lakes, USA) to tens of centimetres (e.g., Lake Chad, Africa), depending on size and wind conditions. In the case of the Aral Sea, contributing E-P (1.5 km3 yr−1), river run-off (3.0 km3 yr−1) and altimetry (1.5 km3 yr−1) errors combine to give a ∼3.5 km3 yr−1 water mass balance error. Of particular interest are those lakes in arid and semi-arid regions where water is an essential economical resource. Anthropogenic influences (irrigation and the construction of dams) may strongly affect lake and inland sea evolution or affect the global water cycle in general, noting the worldwide development of large reservoirs over the last 50 years. With regards to societal and economic issues then, this article reviews several of the case studies focussing on the Aral and Caspian Seas, and Lakes Issykkul and Chad. To cite this article: J.-F. Crétaux, C. Birkett, C. R. Geoscience 338 (2006).
Article
Many inland water investigations utilize archival and near-real time radar altimetry data to enable observation of the variation in surface water level. A multialtimeter approach allows a more global outlook with improved spatial resolution, and combined long-term observations improve statistical analyses. Central to all programs is a performance assessment of each instrument. Here, we focus on data quantity and quality pertaining to the Poseidon-3 radar altimeter onboard the Jason-2/OSTM satellite. Utilizing an interim data set (IGDR), studies show that the new on-board DIODE/median and DIODE/DEM tracking modes are performing well, acquiring and maintaining the majority of lake and reservoir surfaces in varying terrains. The 20-Hz along-track resolution of the data, and particularly the availability of the range output from the ice-retracker algorithm, also improves the number of valid height measurements. Based on test-case lakes and reservoirs, output from the ice-retracker algorithm is also seen to have a clear advantage over the ocean-retracker having better height stability across calm and icy surfaces, a greater ability to gain coastline waters, and less sensitivity to loss of water surface when there is island contamination in the radar echo. Such on-board tracking and postprocessing retracking enables the lake waters to be quickly gained after coastline crossing. Values can range from <0.1 s to 2.5 s, but the majority of measurements are obtained in less than 0.4 s or <2.3 km from the coast. Validation exercises reveal that targets of 150 km2 surface area and 0.8 km width are able to be monitored offering greater potential to acquire lakes in the 100–300 km2 size-category. Time series of height variations are also found to be accurate to 3 to 33 cm rms depending on target size and the presence of winter ice. These findings are an improvement over the IGDR/GDR results from the predecessor Jason-1 and TOPEX/Poseidon missions and can satisfy the accuracy requirements of both the science-related and operational lake study programs.
Article
The Caspian Sea has displayed considerable fluctuations in its water level during the past century. Knowledge of such fluctuation is vital for understanding the local hydrological cycles, climate of the region, and construction activities within the sea and along its shorelines. This study established a point-wise satellite altimetry approach to monitor the fluctuations of the Caspian Sea using a complete dataset of TOPEX/Poseidon for the period 1993 to the middle of 2002, and its follow-on Jason-1 for the period 2002 to August 2009. Therefore, 280 virtual time-series were constructed to monitor the fluctuations. The least squares spectral analysis (LSSA) method is, then employed to find the most significant frequencies of the time-series, while the statistical method of principle component analysis (PCA) is applied to extract the dominant variability of level variations. The study also used the observations of TOPEX/Poseidon and Jason-1 over the Volga River along with 5 years of Volga’s water discharge to study its influence on the Caspian Sea level changes. The LSSA results indicate that the lunar semidiurnal (M2) and the Sun semidiurnal (S2) frequencies are the main tidal frequencies of the Caspian Sea with the mean amplitude of 4.2 and 2.8 cm, respectively. A statistically significant long-term frequency (12.5-years period) is also found from altimetry and tide gauge observations. A phase lag, related to the inter-annual frequencies of the Volga River was detected from the point-wise time-series showing level propagation from the northwest to the southeast of the sea. The cross-correlation between the power spectrum of Volga and that of the northern-most, middle, and southern-most points within the Caspian Sea were respectively 0.63, 0.51 and 0.4 of zero-lag correlation, corroborating the influence of the Volga River. The result of PCA also shows that different parts of the Caspian Sea exhibit different amplitudes of level variations, indicating that the point-wise approach, when employing all available satellite measurements could be a suitable method for a preliminary monitoring of this inland water resource as it gives accurate local fluctuations.
Chapter
Detailed accurate Digital Elevation Model (DEM) data have historically not been available on other than a regional scale, and often have uncertainties in both vertical and horizontal precision. This paper presents the results of a global assessment of the unique Shuttle Radar Topographic Mission (SRTM) DEM using more than 100 million height datapoints derived from ERS1, ERS2, Topex, EnviSat and Jason-1 radar altimeter data, retracked using an expert system approach. This paper outlines the retracking approach taken to derive heights from the altimeter waveforms and describes the methodology for fusion of these data with the SRTM dataset, correcting errors in the SRTM heights and providing accurate measurements beyond the SRTM latitude limit, to produce a full global DEM. Of particular interest, the unique ability of radar altimeters to provide very precise vertical measurements has allowed the correction of vertical offsets to better than 1 m within ACE2, and has also allowed identification of horizontal misplacements. As part of this development, a detailed quality matrix is being generated, to give users information both on the data source of each pixel, and an assessment of the vertical precision of the measurement. It is this detailed global assessment of quality that makes the ACE2 development both unique and of special value for a range of geodetic applications. The first full release of ACE2 is scheduled for later in 2008.
Article
This letter presents an innovative method for computing the wet tropospheric correction for altimetry measurements in the coastal regions, where the measurements from the microwave radiometers (MWRs) onboard altimetric missions become invalid. The method, called Global Navigation Satellite System (GNSS)-derived Path Delay, gives an estimation of the correction, along with the associated mapping error, from the combination of independent zenith wet delay (ZWD) values obtained from the tropospheric delays derived at a network of coastal GNSS stations, from the MWR measurements acquired before land degradation, and from the European Centre for Medium-Range Weather Forecasts Deterministic Atmospheric Model. The wet tropospheric correction is estimated at each altimeter point with an invalid MWR value using a linear space-time objective analysis technique that takes into account the spatial and temporal variability of the ZWD field and the accuracy of each data set used. The method was applied in the South West European region for the whole Envisat data series, and the results are presented here. The uncertainty of the wet-delay estimates is below 1 cm, provided they are obtained for points at distances shorter than ~ 50 km from a GNSS station, and/or valid MWR measurements are available for the estimation. The method can be implemented globally and foster the use of satellite altimetry in coastal studies.
Validation of CryoSat-2 SAR and SARin modes over rivers for the SEOM/SHAPE project
  • N Bercher
  • P Fabry
  • A Ambró Zio
  • M Restano
  • J Benveniste
Bercher, N., Fabry, P., Ambró zio, A., Restano, M., Benveniste, J., 2016. Validation of CryoSat-2 SAR and SARin modes over rivers for the SEOM/SHAPE project. In: Presentation at Living Planet Symposium 2016. May 10 2016, Prague, Czech Republic.
EIGEN-6C4 The latest combined global gravity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and GRGS Toulouse
  • M J Fernandes
  • C Lázaro
  • Christoph
  • Sean L Bruinsma
  • Abrikosov
  • Oleg
  • Lemoine
  • Marty Jean-Michel
  • Jean Charles
  • Flechtner
  • Frank
  • G Balmino
  • F Barthelmes
  • R Biancale
Fernandes, M.J., Lázaro, C., 2016. GPD+ Wet tropospheric corrections for CryoSat-2 and GFO altimetry missions. Remote Sens. 8, 851. Fö rste, Christoph, Bruinsma, Sean. L., Abrikosov, Oleg, Lemoine, Jean-Michel, Marty, Jean Charles, Flechtner, Frank, Balmino, G., Barthelmes, F., Biancale, R., 2014. EIGEN-6C4 The latest combined global gravity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and GRGS Toulouse. 2014. GFZ Data Services. http://dx.doi.org/10.5880/icgem.2015.1.
CryoSat Mission and Data Description
  • C R Francis
Francis, C.R., 2007. CryoSat Mission and Data Description; CS-RP-ESA-SY-0059; ESTEC: Noordwijk, The Netherlands, p. 82.